Caseless pellet igniting mechanism

ABSTRACT

A firing chamber is provided which peripherally surrounds a pellet of caseless propellant at spaced intervals only, with intermediate portions of the pellet being peripherally unsupported. A striking mechanism having a tapered nose for impacting the pellet is provided, with the tapered striker nose being operative to punch out a portion of the pellet and compress that punched out portion against an anvil to ignite that portion. The tapered striker nose is also operative to cause fracturing of the remainder of the pellet along lines generally extending from the punched-out area to the unsupported peripheral portions of the pellet. The fracturing thus induced aids greatly in rapid and complete combustion of the entire pellet.

United States Patent 11 1 1111 3,777,382 Brunelle Dec. 11, 1973 CASELESS PELLET IGNITING MECHANISM Primary ExaminerSamuel W. Engle [75] Inventor: Lawrence J. Brunelle, East Haven, Atmmey wmlam Jones Conn.

[73] Assignee: glin Corporation, New Haven, [57] ABSTRACT onn. [22] Filed: July 20, 1972 A firing chamber is provided which peripherally surrounds a pellet of caseless propellant at spaced intermi 1 vals only, with intermediate portions of the pellet Related Application Data being peripherally unsupported. A striking mechanism having a tapered nose for impacting the pellet is pro [63] gg fgx g g' g giii gsgg g vided, with the tapered striker nose being operative to 45 June 12 1970 Pat No 3 659 punch out a portion of the pellet and compress that s punched out portion against an anvil to ignite that 52 0.8. (:1 42/1 R, 89/7 227/10 P Th6 tapered Striker is also oPerative [51] Int. Cl. BiSc 1/12 cause fracwring of the remainder of the Pellet along 1 19111 of Search 89/7 1 R 42/1 R- generally extending from the P ma 227/9 to the unsupported peripheral portions of the pellet. The fracturing thus induced aids greatly in rapid and [56] References cited complete combustion of the entire pellet. UMTED STATES PATENTS 2 Claims 4 Drawin Figures 3,283,657 11/1966 Kuavle 89/7 g 21 Z 7 r w 't 4 1 7/ M f 7* f 7 1 2 l/'/lf 7oz 1 r *-m l4 ll/ J8 8; F L h" .7

e 1 1 s Q p 6 44 0 45 i I 4/ 24 Z jz PATENTEMEm 1 '91s INVENTOR I LAWRENCEJ BRUNELLE ATTORNEY CASELESS PELLET IGNITING MECHANISM This is a continuation of application Ser. No. 94,835, filed Dec. 3, 1970, now abandoned, which in turn is a continuation-in-part of application Ser. No. 45,651, filed June 12, 1970, now U.S. Pat. No. 3,659,768. 5

This invention concerns a mechanism for firing caseless pellets of propellant material of the type enjoying wide use in the construction industry. Such propellant pellets are commonly used with power actuated tools and devices for driving fasteners into wood, concrete, metal, or other supporting surfaces, and are formed from compacted nitrocellulose with or without a primer material.

Several problems have arisen in connection with the prior art systems for firing caseless propellant pellets which have no metallic case. The problems concern, in particular, the reliability of the pellets. To fire such a pellet, the pellet is seated in a firing chamber adjacent to an anvil member which is generally perforated so that combustion gases produced when the pellet is fired can pass through the anvil and into the barrel to act upon the fastener, in free flight tools, or upon a piston which drives the fastener, in piston-type tools. The firing pin in the mechanism is driven against the seated pellet and thus punches out a segment of the pellet and compresses the punched out segment against the anvil. This punched segment of the pellet is thus ignited to produce a flame which ideally spreads to the remainder of the pellet to consume the pellet and produce combustion gases used to operate the device.

In order for the ignited pellet to produce high pressure combustion gases, the pellet must be confined with a small combustion chamber. If the pellet is not thusly confined, it will merely burn slowly and not quickly produce the combustion gases needed to operate the device. Besides proper confinement of the pellet, another factor which influences the amount of high pressure gases produced, is the speed at which the flame spreads through the pellet to consume it. The spreading of the initially caused flame is greatly enhanced if the pellet is fractured somewhat laterally of the punchedout portion at the same time the punching occurs. Prior artsystems used for firing caseless pellets of this type have recognized the need to confine the pellets, and have included combustion chambers which completely surround the side wall of the pellet and give abutting support thereto through the entire 360 circumference thereof, or the entire periphery thereof should the pellet not be cylindrical. This type of complete peripheral support, however, tends to retard or even completely eliminate the desirable lateral or radial fracturing, and thus requires a longer time period for complete combustion of the pellets. When the combustion gas pressure in this type of device has increased sufficiently to drive the fastener, or the working piston, a sudden pressure drop occurs in the barrel forward of the anvil due to the volume increase resulting from actuation of the device. Thus a vacuum is created forward of the anvil, which vacuum tends to suck the flame through the anvil and out of the combustion chamber. When the combustion chamber. This residue of unburned pellet material hinders reloading of the device for the succeeding shot since the chamber is closely sized to the dimensions of the pellet, and can be dangerous since it can increase the power of the succeeding shot in the event that total combustion occurs therein.

A further problem noted in connection with the prior art devices of the character described concerns the amount of force needed to cock the firing pin and drive it into the pellet. The firing pins of the prior art devices are constructed with flat impacting faces which extend the entire diameter of the cylindrical pin. As a result,

such impacting faces have a relatively large area and 7 punch out a relatively large portion of the pellet. In order to ensure that ignition will result from the punch out, the force per unit area must be comparatively high, thus requiring a stiff firing pin spring to be used. A spring force of about fifty pounds is generally required for use with the prior art devices of the character described. Thus such devices are considerably difficult to cock for firing because of the heavy spring force needed to ensure ignition.

The mechanism of this invention solves the above noted deficiencies in the prior art devices by providing a firing chamber having a side wall which engages the side wall of the pellet in spaced areas only so as to provide less than total peripheral support of the pellet. Thus the pellet, when chambered, has side wall areas which are fully supported alternating with side wall areas which are unsupported. In this manner sufficient support and confinement are provided to permit rapid increase in combustion chamber pressure, and fracturing of the pellet concurrent with punching is induced in portions of the pellet inwardly contiguous with the unsupported side wall areas, the fracturing providing paths or conduits along which flame is quickly propagated from the punched-out part of the pellet.

The firing pin is formed with a nose portion which is frustoconical, e.g., has the form of a truncated cone, so that the truncated surface on the nose is the part of the firing pin which compresses the pellet material against the anvil. In this manner a smaller area than the cross sectional area of the firing pin is used to ignite the pellet so that a weaker firing pin spring can be used to gen erate the necessary force per unit area to ensure ignition of the pellet. A spring force as low as about fifteen pounds has proven satisfactory with the frustoconical firing pin nose, thus considerably reducing the force needed to cock the firing pin. A further advantage has been noted with the use of a firing pin having a frustoconical nose. When the nose of the firing pin pierces the pellet, the flat portion ignites the propellant, and the tapered portion of the firing pin nose wedges through the pellet producing lateral forces which tend to fracture the pellet along lines radiating toward the unsupported peripheral areas of the pellet.

As previously noted, the prior art devices of the character described have displayed a marked tendency toward incomplete combustion of propellant charges because of failure to properly fracture the pellet for flame propagation, and furthermore have displayed a tendency to misfire because of failure to generate sufficient force per unit area on the firing pin impacting face to ignite the pellet. The device of this invention has been fired in tests up to one thousand consecutive times without a single instance of misfire, and with complete combustion of the pellet occuring upon each firin It i s, therefore, an object of this invention to provide a mechanism for the ignition of caseless propellant pellets which mechanism produces complete combustion of pellets fired and substantially eliminates the occurrance of misfire.

It is yet another object of this invention to provide a mechanism of the character described which includes a firing chamber having a side wall providing reduced areas of lateral support for chambered pellets with intervening lateral areas which are free of support for chambered pellets to promote radial fracturing of the pellets toward the unsupported areas when the pellets are struck by a firing pin.

It is further an object of this invention to provide a mechanism of the character described which includes a firing pin member having a nose portion of frustoconical configuration to ensure ignition with a relatively weak firing pin spring force, and to provide a tapered surface for wedging the pellet to promote radial fracture thereof when the firing pin strikes the pellet.

These and other objects and advantages of the invention will become more readily apparent to those skilled in the art from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side view, partially in section of a pistontype power actuated tool utilizing a preferred embodiment of the firing mechanism of this invention for firing caseless pelletized propellant charge; v

FIG. 2 is a side view of the nose portion of the firing pin of the tool of FIG. 1, enlarged and showing the preferred configuration thereof;

FIG. 3 is an enlarged fragmentary view in section of the firing chamber portion of the tool of FIG. 1 after the firing pin has impacted the propellant pellet and punched out a portion thereof to ignite the pellet; and

FIG. 4 is a fragmentary sectional view taken along line 4-4 of FIG. 3 showing more clearly how the firing chamber partially laterally confines the pellet with in termediate unconfined lateral areas, and also showing the radial fracturing which is induced in the pellet by the fi'ring pin nose and side wall of the firing chamber.

Referring now to FIG. 1, a piston-type power actuated tool embodying a preferred form of this invention is shown. The tool includes a housing or receiver portion 2 which is slidably mounted a barrel member 4 having a bushing 5 secured to the forward end thereof. The barrel 4 includes a main bore 8 which has its rearward terminal at a radially inwardly extending shoulder 10. An anvil member 12 is fitted in the bore 8 and seats against the shoulder 10, the anvil 12 being press fitted, welded, or otherwise secured in the bore 8. The anvil 12 includes a plurality of through passages 14 of predetermined area so as to provide sufficient confinement while at the same time providing fluid communication between the bore 8 and a firing chamber in which a propellant pellet 16 is chambered for firing. A bolt member 18 is mounted in the receiver, the bolt member having a nose portion 20 of reduced diameter which is telescopingly received within a counterbore 22 formed in the rearwardmost portion of the barrel member 4. It is noted that the counterbore 22 opens into the firing chamber so that the front face 24 of the bolt 18 is adjacent to and provides support and confinement for the rearward face of the pellet 16. Thus the front and rear surfaces of the pellet 16 are supported and confined by the anvil 12 and bolt 18 respectively. The manner in which the side wall of the pellet 16 is supported and confined will be set forth in greater detail hereinafter. The bolt 18 includes a through passage 26 in which is slidably mounted the stem portion 28 of a firing pin 30. The firing pin 30 includes a radially enlarged shoulder 32 which engages the forward end of a coil spring 34, the rearward end of the firing pin spring 34 being seated against a cap 36 mounted in the receiver 2. It is noted that the rearward end portion of the firing pin 30 is elongated as at 38 and positioned within the spring 34 to form a spring guide. The firing pin spring 34 thus acts to urge the firing pin 30 forwardly toward the pellet 16. A cocking slide member 40 is slidably mounted on the receiver 2 and carries a sear member 42 pivotally mounted thereon by means of a pin 44. A spring member 46 is sandwiched between the slide 40 and the rearward portion of the sear 42 to bias the latter in a counter-clockwise direction about the pin 44. Thus a notch 48 formed-on the sear 42 is urged upwardly into engagement with the shoulder 32 of the firing pin 30. The cocking slide 40 is biased forwardly by a spring member 50, and the slide 40 includes a cross web portion 52 which is contacted by the rear face of the barrel 4. To cock the firing pin 30, the bushing 6 is pushed against a supporting surface S into which a fastener F is to be embedded. In this manner the barrel 4 is pushed rearwardly against the slide web 52 to move the slide 40 and sear 42 rearwardly. Since the sear 42 engages the firing pin 30, the rearward movement of the sear 42 causes the firing pin 30 to move rearwardly to compress the firing pin spring 34 thus cocking the firing pin 30. Push down to cock the device continues until the rearward edge of the barrel 4 contacts the bolt 18.

FIG. 2 shows in detail the configuration of the nose portion of the firing pin stem 28, the nose portion being that portion of the firing pin 30 which impacts the pellet 16. The nose of the firing pin stem 28 is in the form of a truncated cone, or frustoconical in configuration. The stem 28 has a first diameter D which extends to a tapered surface 29 on the nose. The front surface 31 of the firing pin nose is normal to the axis of the stem 28 and has a diameter d which is smaller than the diameter D of the stem 28, the diameter (1 preferably being in the range of 0.040 0.080 inches, and being most preferably about 0.060 in diameter. The tapered surface 29 is preferably disposed at an angle of about 15 to the axis of the stem 28.

FIG. 3 shows the manner in which the firing pin nose acts upon the pellet 16 when the tool is fired. When the trigger 41 is pulled to the rear, the trigger spring finger 43 moves against the sear 42 and causes the latter to pivot in a clockwise direction about the pin 44 disengaging the sear notch 48 from the firing pin shoulder 32 thus freeing the firing pin 30 for forward movement by the firing pin spring 34. As shown in FIG. 3, the frustoconical nose of the firing pin 30 is rammed against the pellet 16, and the flat face 31 of the firing pin nose pierces the pellet 16 and compresses a small portion thereof against the anvil 12 to ignite that small portion of the pellet. Conjointly, the tapered surface 29 on the firing pin nose pierces the pellet l6 and imposes an outwardly radiating wedging force on the pellet 16 in the direction of arrows A. Since the pellets 16 are formed from compacted fibrous or particulate material, such as nitrocellulose, or the like, the pellets are rather frangible.

FIG. 4 shows the manner in which the side wall of the pellet 16 is alternately supported and unsupported in the firing chamber. A generally elliptical opening 54 is formed in the barrel 4 and extends from the shoulder to the counterbore 22. Preferably, the minor diameter of the opening 54 is disposed in a vertical direction, and is approximately equal to the diameter of the pellet 16, to provide top and bottom confinement and support for the side wall of the pellet. Preferably, the major diameter of the opening 54 is disposed in the horizontal direction and is substantially larger than the diameter ofthepellet 1.6..A pair of prongs 56.are formed preferably on the sides of the bolt 18 and extend forwardly fromthe front surface 24 of the bolt nose. The crosssectional configuration of the prongs 56 is such that they slide snugly into the opening 54 in the barrel, with the inner faces 58 of the prongs 56 engaging and providing lateral support and confinement for the lateral portions of the side wall of the pellet 16. In this manner, the side wall of the firing chamber provides support and confinement for the side wall of the pellet 16 at points or portions angularly spaced about 90 apart from the next adjacent areas of support, with there being substantial portions of the side wall of the pellet 16 which are not supported or confined. The outwardly directed wedging force imparted to the pellet 16 by the tapered surface 29 on the firing pin nose is thus not resisted in the non-supported side areas of the pellet 16, with the result that this wedging force causes radial fracturing of the pellet to occur generally as shown at 60 in FIG. 4. These radial fractures provide lateral conduits for propagation of flame from the ignited area of the pellet 16, thus ensuring that the entire pellet will be quickly ignited. At the same time, the wall of the opening 54 and the side walls 58 of the prongs confine the fractured pellet sufficiently to prevent substantial lateral movement of any fragments thereof.

As previously noted, by reducing the area of the fiat, pellet-striking front surface of the firing pin, a substantial reduction in the spring force necessary to drive the firing pin to ignite the pellet is achieved. For example, a firing pin requiring a spring having a fifty pound spring force to ignite a pellet, can ignite the same pellet with a spring having afifteen pound spring force if the firing pin nose is frustoconically shaped in the manner shown. Furthermore, by providing a firing chamber which has only partial confinement and support of the lateral face of the pellet, with intervening areas of nonsupport, and by impacting the pellet with a firing pin having a frustoconical nose, lateral fracture of the pellet is achieved to provide channels or paths for propagating flame to ensure complete combustion of the pellet in a short time period.

Since many changes and variation of the disclosed embodiment of the invention may be made without departing from the inventive concept, it is not intended to limit the invention otherwise than as required by the appended claims.

What is claimed is:

1. In a tool operated by firing a generally disc-shaped pellet of combustible material, which pellet includes transverse front and rear surfaces and a generally cylindrical side surface, a chamberingand firing mechanism comprising:

a. a firing chamber for containing the pellet, said firing chamber including transverse front and rear wall parts for confining the transverse front and rear surfaces of the pellet, and a side wall comprismg:

i. first side wall means extending between said front and rear wall parts, said first side wall means being operative to engage the cylindrical side surface of the pellet; and

ii. second side wall means extending between said front and rear wall parts, said second side wall means being circumferentially interposed between said first side wall means, and said second side wall means, as measured from the longitudinal axis of the firing chamber, being radially outwardly offset from said first side wall means and from the cylindrical side wall of the pellet when the latter is chambered for firing, to provide separate areas of the cylindrical side wall of the pellet which are free of contact with said side wall of said firing chamber and said separate areas forming circumforential voids; and

b. means for igniting the pellet adjacent said firing chamber, and operative to pierce and compress a portion of the chambered pellet to ignite the latter and concurrently effect fracturing of the pellet which fracturing radiates toward the areas of the cylindrical side wall of the pellet which are free of contact with said side wall of said firing chamber.

2. The chambering and firing mechanism of claim 1, wherein said means for igniting the pellet is a firing pin having a predetermined cross-sectional area and a nose portion of frustoconical configuration providing a flat end wall having an area smaller than said predetermined cross-sectional area.

;,U1 -:1TEDs'1'ATEs PATENT OFFICE CERTIFICATE ()F CORREQTION Patent No. 3,777,382" e Dated December 11, 1973 Invento'fls) Lawrence J Brunelle It is certified that error appears in the above-identified patent and that said Letters Patentere hereby corrected as shown below:

In Col. 1, line 32, "with" shouldread ---within--;

111 4, line 47 "inches" should read --inch--;

In Col. 5, line 37, after "prmngs" please insert --56--.

Signed and sealed this 1st day of October ,1974,

(SEAL) Attest:

MCCOY M. GIBSON JR. 0. MARSHALL ZDLANN Atte'sting Officer Commissioner of Patents USCOMM-DC 60376-P69 FORM PC4050 (0-69) 1 e n 0.5. covznmum rnnmuc OFFICE was o-ass-au I ;.UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,777,382 Dated December 11, 1973 lnv' n fl Lawrence J Brunelle It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Col. 1, line 32, "with" should, read --within--;

C01. 4, line 47,'- "inches" should read --inch- In Col. 5, line37, after "prongs" please insert --56--.

e Signed and sealed this 1st day of October 1 1974.

(SEAL) Attest: I

MCCOY M. GIBSON JR. 0. MARSHALL DiANN Attesting Officer Commissioner of Patents FORM F o-i059 (10-69) USCOMM-DC 60376-P69 U. 5. GOVERNMENT PRINTING OFFICE HID 0--366-.!J4 

1. In a tool operated by firing a generally disc-shaped pellet of combustible material, which pellet includes transverse front and rear surfaces and a generally cylindrical side surface, a chambering and firing mechanism comprising: a. a firing chamber for containing the pellet, said firing chamber including transverse front and rear wall parts for confining the transverse front and rear surfaces of the pellet, and a side wall comprising: i. first side wall means extending between said front and rear wall parts, said first side wall means being operative to engage the cylindrical side surface of the pellet; and ii. second side wall means extending between said front and rear wall parts, said second side wall means being circumferentially interposed between said first side wall means, and said second side wall means, as measured from the longitudinal axis of the firing chamber, being radially outwardly offset from said first side wall means and from the cylindrical side wall of the pellet when the latter is chambered for firing, to provide separate areas of the cylindrical side wall of the pellet which are free of contact with said side wall of said firing chamber and said separate areas forming circumforential voids; and b. means for igniting the pellet adjAcent said firing chamber, and operative to pierce and compress a portion of the chambered pellet to ignite the latter and concurrently effect fracturing of the pellet which fracturing radiates toward the areas of the cylindrical side wall of the pellet which are free of contact with said side wall of said firing chamber.
 2. The chambering and firing mechanism of claim 1, wherein said means for igniting the pellet is a firing pin having a predetermined cross-sectional area and a nose portion of frustoconical configuration providing a flat end wall having an area smaller than said predetermined cross-sectional area. 